Optical access network
An object of the present invention is to provide an optical access network that has high reliability for supporting information communication services and efficiently responds to difficult-to-predict optical fiber demand. An optical access network configuration according to the present invention includes an optical fiber cable 11 that is looped to connect a wiring section 25 and an exchange office 10 together (hereinafter, an upper loop), an optical fiber cable 21 that is looped and laid in each wiring section 25 (hereinafter, a lower loop), and an optical fiber switching function unit 31 installed at a connection point 30 between the upper loop 11 and the lower loop 21 . The optical fiber switching function unit 31 is a wiring board or an optical switch which can be switched by connector connection. The wiring board or the optical switch may be remotely controllable.
1. An optical access network comprising:
an upper loop optical fiber cable which includes a plurality of fixed station lines and at least one common line and is laid on a loop-like path passing through a communication carrier base facility; and
a lower loop optical fiber cable of a plurality of lower loop optical fiber cables which includes at least one user line and at least one redundant line and is laid on a loop-like path passing through a connection point with the upper loop optical fiber cable and a user base facility,
wherein
a fixed connection line for connecting the user line and the fixed station lines in a 1:1 ratio, and an optical fiber switching function unit for exclusively connecting the redundant line and the common line are provided at the connection point,
the number of the common lines is smaller than the total number of the redundant lines included in each of the plurality of lower loop optical fiber cables, and
the optical fiber switching function unit switches connection between the redundant line and the common line according to demand fluctuation of the lower loop optical fiber cable.
2. The optical access network according to claim 1 , wherein the loop-like path of the upper loop optical fiber cable is a path in which an improvement rate γ of availability in a case of the upper loop optical fiber cable is maximized with respect to availability when there is one path from the communication carrier base facility to the connection point in a wiring section where the lower loop optical fiber cable is laid.
3. The optical access network according to claim 2 , wherein the improvement rate γ expressed by Expression C1, and
the loop-like path of the upper loop optical fiber cable is r loop that maximizes the improvement rate γ:
[
Math
.
C1
]
γ
=
C
1
C
2
σθ
r
loop
(
R
2
-
r
loop
2
)
2
+
C
1
C
2
σθ
r
loop
(
R
2
-
r
loop
2
)
(
C1
)
where an area shape constructed by the upper loop optical fiber cable is a fan shape having a center angle θ and a radius R with the communication carrier base facility as an origin, the r loop is a distance from the communication carrier base facility to the connection point, σ is a demand density, and C1 and C2 are constants.
4. The optical access network according to claim 1 , wherein the number of optical fibers connecting the redundant line and the optical fiber switching function unit is a number that converges the number of optical fibers F total included in the upper loop optical fiber cable to a minimum.
5. The optical access network according to claim 4 , wherein the optical fiber number F total is calculated by Expression C2:
[
Math
.
C2
]
F
total
=
∑
i
=
1
N
(
1
-
a
i
)
f
i
+
F
c
(
C2
)
where N is the number of the lower loop optical fiber cables connected to the upper loop optical fiber cable, a i is the proportion of the number of the redundant lines among the optical fibers included in the i-th lower loop optical fiber cable (hereinafter, flexible optical fiber ratio), and f i is an optical fiber included in the i-th lower loop optical fiber cable, and Fc is the number of the common lines, here, f i satisfies Expression C3, and Fc satisfies Expression C4,
[
Math
.
C3
]
∑
2
f
i
k
=
0
p
i
,
k
≥
x
(
C3
)
x is a design value of reliability per wiring section where the lower loop optical fiber cable is laid, and p i, k is a probability that the number of demand generated in the i-th wiring section is k-core,
[
Math
.
C4
]
∑
2
F
c
k
=
0
q
N
,
k
≥
x
N
(
C4
)
q N, k is a probability that the total of the demand number exceeding the fixed station lines in the 1st to N-th wiring sections calculated by Expression C5 is k-core,
[
Math
.
C5
]
(
Case
of
N
=
1
)
q
1
,
k
=
p
1
,
(
1
-
a
)
f
i
+
k
(
Case
of
N
>
1
)
q
N
,
k
=
∑
l
=
0
k
q
N
-
1
,
l
p
N
,
(
1
-
a
)
f
i
+
k
-
1
.
(
C5
)